[pdonis]

> the original instruction was "straight line", not "geodesic"

If you're working within a 2-sphere, such as the Earth's surface, or indeed any non-Euclidean geometry, they mean the same thing. More precisely, there are no "straight lines" in the exact sense you mean in a non-Euclidean geometry, but there are geodesics that satisfy all of the geometric properties of "straight lines" within that non-Euclidean geometry.

[lxgr]

Nowhere did TFA define that we're working within a 2-sphere, though!

[pdonis]

Yes, it did:

"Then start traveling forward, in a straight line along the Earth’s surface."